HCA-Sand¶

The high-cycle accumulation (HCA) model of Niemunis, Wichtmann & Triantafyllidis. Rather than resolving every load cycle, the HCA model computes the accumulation of strain (or stress) as an explicit function of the number of cycles, the strain amplitude, the void ratio, the mean pressure and the cyclic preloading. It is calibrated against HCA tests and is the tool of choice for very large cycle numbers (e.g. offshore foundations).

At a glance

Class: ACT.models.HCA_sand
numgeo name: HCA_sand
Parameters with search bounds: 15
Imported as: from ACT.models import HCA_sand

Units and angles

Enter phi in radians and patm in kPa. epsampl_ref is a strain fraction. Abulk is the dimensionless elastic coefficient \(A\), not a stress or modulus; the other bounded HCA parameters are dimensionless. Pore-fluid bulk modulus supplied by an HCA test is in kPa.

Default search bounds¶

These are the built-in lower/upper bounds used when a parameter is optimized. Override any of them with set_bounds.

Parameter	Lower	Upper	Description
`CN1`	1e-5	1e-2	cyclic strain-accumulation parameter
`CN2`	5e-3	2	cyclic strain-accumulation parameter
`CN3`	0.	5e-4	cyclic strain-accumulation parameter
`Campl`	1.	3.	amplitude-function parameter
`Ce`	0.2	1.	void-ratio-function parameter
`Cp`	-5e-2	1.	pressure-function parameter
`Cy`	1	5.	cyclic-preloading-function parameter
`patm`	0.	1e5	atmospheric reference pressure
`eref`	0.2	2.	reference void ratio
`epsampl_ref`	1e-5	1e-2	reference strain amplitude
`Abulk`	500	2e3	dimensionless elastic coefficient \(A\)
`abulk`	1.	3.	dimensionless elastic exponent \(a\)
`nbulk`	0.2	0.8	bulk-modulus exponent
`nu`	0.25	0.48	Poisson's ratio
`phi`	0.3491	0.62832	friction angle (radians)

Setting parameters¶

Assign initial / fixed parameter values with set(...):

from ACT.models import HCA_sand

model = HCA_sand()
model.set(CN1=..., CN2=..., CN3=..., Campl=..., Ce=..., Cp=...)

Full set signature

set(CN1=None,CN2=None,CN3=None,Campl=None,Ce=None,Cp=None,Cy=None,patm=None,eref=None,epsampl_ref=None,Abulk=None,abulk=None,nbulk=None,nu=None,phi=None)

Available set parameters: CN1, CN2, CN3, Campl, Ce, Cp, Cy, patm, eref, epsampl_ref, Abulk, abulk, nbulk, nu, phi.

Choosing free parameters¶

Narrow the search interval of selected parameters, then list the ones to optimize in globals.setup:

model.set_bounds(CN1=[1e-5, 1e-2], CN2=[5e-3, 2], CN3=[0., 5e-4], Campl=[1., 3.])
globals.setup(Model=model, Free_parameter=["CN1", "CN2", "CN3", "Campl", "Ce", "Cp"], ...)

Parameters that accept a set_bounds override: CN1, CN2, CN3, Campl, Ce, Cp, Cy, patm, eref, epsampl_ref, Abulk, abulk, nbulk, nu, phi.

Reading & updating single parameters¶

model.update("CN1", value)   # set one parameter
x = model.get_parameter("CN1")  # read one parameter

See the models overview for the common interface shared by all models, and Optimization for how the free parameters are searched.